Atmospherical Electricity/. 13 



number of lightning-conductors equal to the number of trees 

 felled ; it is tlie modification of the electrical state of an en- 

 tire country ; the accumulation of one of those elements in- 

 dispensable to the formation of hail, in a locality where, pre- 

 viously, this element was dissipated by the silent and inces- 

 sant action of the trees. On this point, observations sup- 

 port theoretical deductions. 



According to a detailed statistical account, the losses oc- 

 casioned by hail in the continental states of the king of Sar- 

 dinia, from 1820 to 1828 inclusively, amount to the sum of 

 forty-six millions of francs. Three provinces, those of Val 

 d'Aoste., the Vallee de Suze, and Haute Maurienne^ do not ap- 

 pear in these tables ; they were not visited with hail storms. 

 The mountains of these three provinces are the best wooded. 



Of the warmest provinces, that of Genoa, the mountains 

 of which are well covered, is scarcely ever visited by this 

 meteor. 



Atmospheric electricity gives rise to phenomena, which 

 are immense from their extent. They seem, however, to owe 

 their origin to causes purely local. Their propagation like- 

 wise takes place under circumscribed influences, in particu- 

 lar zones, and these sometimes rather narrow. 



On the 13th July 1788, in the morning, a hail-storm com- 

 menced in the south of France., traversed, in a few hours, the 

 whole length of the kingdom, and thence extended to the 

 low countries and Holland. 



All the districts in France injured by the hail, were situated 

 in two parallel bands, running south-west and north-east. 

 One of these bands was 175 leagues long ; the other about 

 200. 



The mean breadth of the most western hail band was 4 

 leagues, the other only 2 leagues. On the space between these 

 two bands, rain only fell ; its mean breadth was 5 leagues. 

 The storm moved from the south to the north with a rapidity 

 of about 1 6 leagues an hour. 



The damage occasioned in France, in the 1039 parishes 

 visted by the hail, appeared, from official inquiry, to amount 

 to twenty-five millions (one million sterling.) 



